--- title: "Quarter turn stair, 5.5 m by 4.0 m" subject: "Building Technology" chapter: 5 key: "semester_6/building_technology:quarter-turn-stair-residential-lobby" source: https://www.bctengineer.com/q/semester_6/building_technology/quarter-turn-stair-residential-lobby site: BCT Engineering --- # Quarter turn stair, 5.5 m by 4.0 m Building Technology · Chapter 5: Stair, lifts and escalators - Asked in: 2075 Baisakh, 1+6+1 marks - Video: [Quarter Turn Stairs with Landing Example #1](https://www.youtube.com/watch?v=Y7LdbloRY5Y) — Luc Lapierre - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/building_technology/quarter-turn-stair-residential-lobby - Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-5 ## Question Define stair. Design a quarter turn staircase for a residential building in a lobby of size 5.5m * 4.0 m. The height of floor to floor is 3.0 m. Assume necessary data if required. Draw neat plan to justify your design. ## Short answer Quarter-turn stair with 20 risers of 150 mm, treads 250 mm, flights of 12 and 8 risers, flight width 1.1 m. ## Answer #### Stair A **stair** is a set of steps (a series of risers and treads) that connects floors at different levels, giving access from one storey to another, usually with landings and a balustrade. #### Design of quarter turn stair #### Given data and assumptions - Stairwell (internal): 5.5 m x 4 m; floor-to-floor height $H = 3$ m; stair for a residential building, RCC. - Assumed riser $R = 150$ mm and tread $T = 250$ mm; flight width $b = 1.1$ m. #### Design 1. **Number of risers** $= H/R = 3/0.15 = 20$, adopt **20 risers**; exact riser $= 3/20 = 150$ mm. 2. **Flights:** a quarter-turn stair has a square quarter landing. Take flight 1 = 12 risers (11 treads) and flight 2 = 8 risers (7 treads); total 12 + 8 = 20 risers. 3. **Goings:** flight 1 $= 11 \times 0.25 = 2.75$ m; flight 2 $= 7 \times 0.25 = 1.75$ m. 4. **Quarter landing:** 1.1 m x 1.1 m at height $= 12 \times 0.15 = 1.8$ m. 5. **Fit along the length:** $2.75 + 1.1 = 3.85$ m $\le 5.5$ m. 6. **Fit along the width:** $1.1 + 1.75 = 2.85$ m $\le 4$ m. 7. **Check:** $2R + T = 2 \times 150 + 250 = 550$ mm (within 550-650 mm); pitch $= \tan^{-1}(R/T) = 31^\circ$ (within 25-40 degrees). 8. **Waist slab:** effective span about 3.85 m, so depth $\approx$ span/20 $= 192$ mm; adopt a 200 mm thick waist slab (reinforcement to be designed separately). Provide a handrail 0.9 m high, 20-25 mm nosing and a non-slip finish. #### Plan and section ```text +----+--------------------+ | F2 | | | ^ | | | ^ | (hall) | +----+--------------------+ |LAND| <<<<<<<<<<<< F1 UP | +----+--------------------+ F1 = 12 risers (starts at the right end), quarter landing, F2 = 8 risers (arrows point up the stair) ``` ```text SECTION (not to scale) +---- upper floor 3 m _____| ____| flight 2 ______| landing ____| flight 1 _| ground floor +0.00 ``` #### Summary | Item | Adopted | |---|---| | Riser | 150 mm (20 nos.) | | Tread | 250 mm | | Flights | flights of 12 and 8 risers | | Width of flight | 1.1 m | | Waist slab | 200 mm | **Answer: 20 risers of 150 mm and treads of 250 mm; flights of 12 and 8 risers; flight width 1.1 m.** ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. A stair is A. A series of risers and treads connecting floors at different levels B. A moving belt C. A mechanical car D. A ramp Answer: A. A stair is a set of steps joining levels, usually with landings and balustrade. (Key point: Definition) 2. 20 risers in this quarter-turn stair are divided into A. 10 and 10 B. 12 and 8 C. 14 and 6 D. 15 and 5 Answer: B. Flight 1 has 12 risers, flight 2 has 8, with a quarter landing. (Key point: Flight split) 3. Quarter landing size and height are A. 1.1 m x 1.1 m at 1.8 m B. 2.2 m x 1.1 m at 1.5 m C. 1.1 m x 1.1 m at 3 m D. 0.9 m x 0.9 m at 1.0 m Answer: A. Landing is square, flight width b = 1.1 m, at 12 x 0.15 = 1.8 m. (Key point: Quarter landing) 4. Going of flight 1 with 11 treads of 250 mm is A. 2.5 m B. 2.75 m C. 3.0 m D. 1.75 m Answer: B. 11 x 0.25 = 2.75 m. 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